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Old 07-01-2009, 01:32 AM
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Chev 350 Int vs Ext balance, engine info.

Now that i have given up all hope of finding the vibration in my present 350 thats in my 65 Elky (see harmonic balancer thread), I am trying to find out as much as I can about my replacement engine, which i also can't get info from the previous owner on. It is a 80-85 block, with stock 1972 small valve 76cc heads. I have found basic info on the block and heads on the web.
The block has 4.00 bore, I have seen the pistons thru the plug hole and they appear in good shape to the naked eye. They are flat with valve notches cut in them, are these standard low comp. pistons? , I would like to change to 2.02 64cc heads in the future to up comp ratio, would the larger valves cause a problem with these pistons?
The pan is off and the bottom end and rods appear to be in very good condition, again to naked eye. My question on the crank is if its internal or ext balance? The large weigths at the front and rear, have what resembles counter sink dimples, not very deep, in both. The crank has the number 3982442 cast in it, is there anywhere to get info by the number on the crank?
The balancer is the large 8" balancer, which appears to be stock and lines up with piston TDC right on, does not have any visible weights on it. However the flywheel that was given me seperately has 1 weight welded to the engine side of it, also it doesn't appear to have a bolt pattern for my 350 turbo trans. I have a feeling the flywheel doesn't belong to this engine and a replacement would not be a great expense anyway. Any help you can give me, or direction to where I might get this info. would really be welcome, hope I have given enough info. to get some answers.
Thanks as always, Crash

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Old 07-01-2009, 01:49 AM
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Your "replacement" 350 is INTERNALLY balanced. But, you say you're not sure the flywheel in your El Camino is the original. First of all, before you do anything else, be sure there are NO balance weights on that flywheel (or flexplate). I won 't go into the problems I had with a stroker 305/334, but trust me, don't get stuck with the wrong flywheel (or flexplate).
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Old 07-01-2009, 02:08 AM
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Your crank is prolly casting number 3932442, not 3982442. If so, it is a large journal, cast, 3.48" stroke w/a 2-piece rear main seal. It was used for 305 and 350 SBC engines from '68-'85.

If the flexplate has a weight attached to it, it is not for the 350 crank and engine.

All you should need to do, is replace it w/a non-counterweighted flexplate for an internal balanced SBC.

These come w/NO WEIGHT attached, and are either a 153 tooth 12-3/4" flywheel/flexplate that uses a straight across pattern starter, or a 168 tooth 14" that uses a staggered pattern starter.

As for the valves, any time a change is made- cam, heads, valves, pistons- it's required that you check the clearances between the valves and piston and piston to head, if their changed.

A cam swap means checking the spring bind, installed height, installed and open pressure and retainer to seal or valve guide clearance, etc.

Below is a photo of both sides of a 400 balancer. Notice the cutaway around the circumference. This is what makes it an externally balanced damper.
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Old 07-01-2009, 07:31 AM
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int vs ext balance engine info

Thanks, you are correct the number is 3932442, things look different in the light of day.
Flywheel has got an approx 7" weight on one side of flexplate, so thats out.
There is no cutout on the balancer, rubber looks cracked so I will probably replace that too. Should I stick with the 8" or go with the smaller balancer?
The starter pattern has 2 threaded holes inline on the rear edge of the block, and 1 hole forward and slightly out of line with the corresponding rear hole, would this be the staggered pattern?
If I buy the new 2.02 heads and theres too little clearance, what are my options? Is it even fesibile to try and get more juice from this engine?
Sorry for so many stupid questions, but I'm on a VA pension and can't afford mistakes.
Thanks for the help, Crash
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Old 07-01-2009, 07:57 AM
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One piece seal 350 is Externaly Balanced just the Flywheel only.
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Old 07-01-2009, 12:33 PM
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int vs ext

Sorry forgot to mention its a 2 piece seal.
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Old 07-01-2009, 01:00 PM
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The weighted flexplate/flywheel is your vibration problem. It should be non-wieghted (neutral balance) to go with that crankshaft. What you have now is for either the 400 SBC or the 454 BBC or maybe one of the 90 V6's that are external balance.

Last edited by ericnova72; 07-01-2009 at 02:01 PM.
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Old 07-01-2009, 01:34 PM
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Quote:
Originally Posted by ericnova72
The weighted flexplate/flywheel is your vibration problem.
This is a "replacement" engine that is not the Vibro-Matic that's installed in the El Camino, if I understood the OP's first post in this thread.

The replacement came w/the externally balanced flex (not installed), too bad this wasn't the V-M engine, or the blame could be laid on the flexplate.

Quote:
Should I stick with the 8" or go with the smaller balancer?
Stick w/the 8", if for no other reason, the timing tab will work the same.

Quote:
The starter pattern has 2 threaded holes inline on the rear edge of the block, and 1 hole forward and slightly out of line with the corresponding rear hole, would this be the staggered pattern?
Yes, you have both patterns so you can use either flexplate.

Quote:
If I buy the new 2.02 heads and theres too little clearance, what are my options? Is it even fesibile to try and get more juice from this engine?
There's potential in this engine. What needs to be discerned is what the deck height is, and what type pistons you have (true flat tops or dished) to tell about what the CR will be w/various chamber sizes of the heads you may be thinking of using.

The heads having 2.02" intakes isn't the real concern. It is what lift the cam will have. A stock cam will not have a clearance problem 99% of the time when using 2.02's. But w/a higher lift cam, there could be issues- that's why you need to measure things.

Lastly, you need to determine if the replacement engine is in good enough condition, wear-wise, to consider adding speed parts to it. If it's tired, I'd advise against modifying it unless it's rebuilt or at least refreshed w/new oil pump, gaskets, seals, bearings and rings/honed cylinders, etc.

When you get the heads off, you can tell how much the bore is worn and whether it has already been bored.

You have the pan off, so you can check the bearings and crank journals to see what's up there.
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Old 07-01-2009, 01:35 PM
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Quote:
Originally Posted by crash
Now that i have given up all hope of finding the vibration in my present 350 thats in my 65 Elky (see harmonic balancer thread), I am trying to find out as much as I can about my replacement engine, which i also can't get info from the previous owner on. It is a 80-85 block, with stock 1972 small valve 76cc heads. I have found basic info on the block and heads on the web.
The block has 4.00 bore, I have seen the pistons thru the plug hole and they appear in good shape to the naked eye. They are flat with valve notches cut in them, are these standard low comp. pistons? , I would like to change to 2.02 64cc heads in the future to up comp ratio, would the larger valves cause a problem with these pistons?
The pan is off and the bottom end and rods appear to be in very good condition, again to naked eye. My question on the crank is if its internal or ext balance? The large weigths at the front and rear, have what resembles counter sink dimples, not very deep, in both. The crank has the number 3982442 cast in it, is there anywhere to get info by the number on the crank?
The balancer is the large 8" balancer, which appears to be stock and lines up with piston TDC right on, does not have any visible weights on it. However the flywheel that was given me seperately has 1 weight welded to the engine side of it, also it doesn't appear to have a bolt pattern for my 350 turbo trans. I have a feeling the flywheel doesn't belong to this engine and a replacement would not be a great expense anyway. Any help you can give me, or direction to where I might get this info. would really be welcome, hope I have given enough info. to get some answers.
Thanks as always, Crash
You're in an area of not really having enough information. Lets knock the flexplate out first, that is you need to know whether it neutral balances with the attached counter weight or not. It's presence doesn't necessarily mean its a 400 external weighted or a 350 1 piece seal wheel. A simple old fashion static bubble type tire balancer will work to see what it is. There are 2 torque converter bolt patterns, some flex plates have one or the other, some have both.

Compression and Valves

These need to be carefully considered, starting with valves where GM sights a casting number, often there is more than one size valve used, this makes a part number which isn't noted on your head so the only way to know what valve sizes are there is to pull a head and look. If your running on the street, even with a pretty aggressive engine on the street, the factory's most often used valve on the 350 of 1.94 and 1.5 inches is plenty good. While big valves sometimes improve top end breathing, they take bottom and mid RPM breathing away because the larger open area slows mixture speeds which reduces cylinder filling as the mixture isn't fast to respond when the valve opens and if you're running much of a cam with late closing intake timing, the piston pushes the mixture back into the intake. These events can really cripple low and mid range torque. So valve size and with it cam timing and compression need to be carefully considered around how the engine is used and where you need power.

Compression is not simple and with the limited octane range of modern fuels and the variable behavior of different brands of same rated octane fuel to the effects of pressure and temperature, compression needs to be carefully considered. Static compression, and dynamic for that matter, have many web based calculators, there is a good one at Keith Black/Silvolite pistons web site. The most common way is to compute Static Compression Ratio (SCR) which is the ratio of the all volumes divided by the volumes above the piston, including the effects of domes, valve reliefs, or dishes in the piston. This calculation needs to include the effects of distance of the piston pin to the piston's crown. Most aftermarket pistons shorten this distance by .020 inch as an a assumed compensation for milling the block's head deck, so called zero clearancing or zero decking the block. Other important considerations are whether the block was decked and by how much, milling doesn't necessarily lead to zero decks even though they're called that. Blocks machined by neighborhood shops then to take off only what's required to get a flat deck, while blocks that passed thru the big time rebuilder shops tend to have been uniformly all milled by .020 to .025 inch. But this doesn't necessarily make a zero deck block either as the 1.540 height replacement piston will still be .020-.025 under the milled deck, where, if the engine got stock 1.56 height pistons and a .020-.025 milled deck, it will have a true zero deck block and higher than stock compression with the same heads on either engine. This is because what counts for makeing a zero deck is the measured distance between the piston crown at TDC and the deck. So you need to know whether the block has been decked and if so by how much and you need to know the piston by part number to determine the pin to crown height. The distance from the piston crown to the block deck, also, along with the head gasket determines the clearance (or compression clearance) between the piston crown and the cylinder head's squish/quench distance. This distance has a great affect on the engine's resistance to detonation and efficiency/power. The goal is to have this not less than .040 inch nor more than .060 inch. Point 040 as a minimum is need with a steel connecting rod to be sure the piston doesn't collide with the cylinder head. The .060 inch number is the top end of best effectivity of squish and quench. So all this needs to be known and computed before deciding your just going to get a smaller chambered head. Also, different heads and pistons for that matter have different tolerance to SCRs/DCRs. So called fast burn chambers such as the Vortec are good for a ratio higher than usually found in stock SMOG era engines, peaking about 9.0 to 9.2 to 1. The same thing in aluminum will usually take a ratio higher without protest because aluminum dissipates heat faster than cast iron. In piston selection, you want a flat area on the piston crown to be across from the squish/quench deck of the head for maximum effect of squish and later quench in the compression/ignition cycle. So the best pistons are flat tops or D dishes/cup where any compensating additional volume of a dish in the piston crown is carried below the valve pocket where it's necessary to keep the overall SCR in the range of 9.2 to 10.5 for cast iron or aluminum heads as previously stated.

Visual Observation of condition:

Not worth much, we're talking a few thousandths of an inch between good and bad parts, this isn't something the human eyeball can do without precision measuring tools.

Bogie
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Old 07-01-2009, 01:58 PM
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Quote:
Originally Posted by crash
Sorry forgot to mention its a 2 piece seal.
Actually, you already did. "It is a 80-85 block" from your first post says it all.
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Old 07-01-2009, 07:12 PM
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int vs ext balance

Thanks, you are correct on my previous post refering to the installed engine., and for answering all my other probs, by flex exam thru plug hole pistions are flat with 2 sets of valve reliefs opposite each other (4 total per piston). The engine was supposedly rebuilt by the guy before the guy I bought it from, and has never been installed.
I'll stick with the 8" as you suggest. I'm not going to go wild performance wise, just want it to breathe a little more.
I'm going to do a comp test on the stand just to get a general idea of condition.
Thanks, crash
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Old 07-01-2009, 09:16 PM
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If you have a torque wrench available to you, I would still want to pull a random rod and main cap- at least one of each.

This will not be a replacement for mic'ing everything and is not intended to be. It will, however, tell you whether or not the bottom end was gone through, whether the crank has been turned and the general condition of the bearings and journals.

By looking at the backside of the bearings you will be able to tell if and how much the crank was turned (99% of the time, a size will be inscribed, if they are for a turned crank).

And by looking at the bearings and crank journals you will see what the condition of it is, AFA abnormal wear patterns, scoring, overlay scuffing and/or erosion from dirt, or other wear, discoloration from overheating, etc. A LOT can be told by a simple visual examination, IMO.

Beginning at PAGE 4 , this guide from Clevite shows some visual clues to various bearing wear patterns and the causes for them.

Among the things Clevite shows visual examples of, are:

NORMAL WEAR
FOREIGN PARTICLES IN LINING
FOREIGN PARTICLES ON BEARING BACK
SHIFTED BEARING CAP
EXCESSIVE CRUSH
INSUFFICIENT CRUSH
BENT OR TWISTED CONNECTING ROD
FILLET RIDE
DISTORTED CRANKCASE
BENT CRANKSHAFT
OUT-OF-ROUND BORE
OUT-OF-SHAPE JOURNAL
OIL STARVATION
HOT SHORT
SURFACE FATIGUE
CORROSION
ACCELERATED WEAR
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Old 07-02-2009, 07:39 PM
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int vs ext balance

Thanks, I will do that I was afraid I'd screw something up if I took them out and put them back again.
That should give me an idea if this guy was telling me the real deal on the engine, he's a racer and had it in his shop as a spare if he needed it, but we're not real tight so anythings possible. I'm hopeing for the best for a change.
As a side note I was playing with my new timing light this am and I advanced the timing about 10 more BTDC on the vibra matic and the vibration seems to be gone, the only other thing I did at the same time was switch air cleaners from foam pro-flo to open 14" Edelbrock. I'm sure this had nothing to do with it. I was only able to give it a short street test as traffic was already heavy, there was no knock. I also noted a very slight misalignment between the water pump pulley and the alternator which seems to have to come away from the block a little to line up the belt.
I bought one of those lights with a degree adj knob on the end, but have no idea how it works as the instructions just tell you how to use a timing light, and doesn't even mention the knob, and their support line is closed for the Holiday.
I will do more testing to be sure, and check out the spare engine on Monday, after all our holiday guests have gone home, guests are sop here in the sunshine state.
Have a happy and safe holiday, and again thanks for the advice. Crash

Last edited by crash; 07-03-2009 at 10:13 AM. Reason: Add'l info
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